Thermal cooled vacuum form

ABSTRACT

A method for preparing a mold form includes forming a mold blank having a surface corresponding to the surface of the article desired and enclosing the mold blank in an open ended enclosure. A thin layer of polymer resin, preferably polyurea is sprayed on the surface of the mold blank and allowed to cure. Heat transfer tubing is inserted over the resin layer. A mixture of metallic pellets and epoxy are inserted over the heat transfer tubing and then another layer of resin is sprayed over the mixture. After the resin has cured, the mold blank is removed to expose the mold form having an outer surface of polyurea.

RELATED APPLICATION

This application is a divisional application of co-pending U.S. patentapplication Ser. No. 09/211,957, filed Dec. 15, 1999.

The present invention generally relates to the manufacture of moldedparts and in particular a thermal cooled mold form.

BACKGROUND OF THE INVENTION

Conventionally, mold forms are manufactured from such materials asaluminum, steel or wood. In the case of steel and aluminum, expensivecasting or cutting machinery is required for producing the final formedshape. After the design is formed, the mold requires hand finishing tofinalize certain complex features of the mold. Further, cooling passagesmust then be installed into the steel or aluminum to provide means formaintaining the mold within a certain temperature range during its use.As a result, a large or complicated mold may require many weeks tocomplete. Although steel or aluminum molds provide a high quality moldform, the life use of these types of molds may exceed the life of thefinal product production. Therefore, in many cases a steel or aluminummold is very expensive relative to the benefits of the final moldedpiece.

Wood molds are undeniably cheaper than the aforementioned steel oraluminum molds, but still requires a labor intensive manufacturingprocedure to produce a quality mold. A wood mold involves no coolingsystem, thereby causing excessive press time in the manufacturingprocess. Wood tools, without a cooling system, causes unpredictableshrinkage in the manufactured part. The durability of wood tools is veryshort.

It is therefore desirable to provide a mold and a method forconstructing the mold which can be manufactured quickly, and at lesscost to the manufacturer without measurably affecting durability.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned concerns by providinga mold having a mold surface made of a polymer resin, in particularpolyurea or a polyurea blend, polyurethanes or a polyurethane blend. Theprocedure to manufacture the mold piece includes forming a wax or woodpattern having a surface of the shape of the final molded piece, andthen building a box structure around the wax or wood pattern. The wax orwood pattern is then sprayed with a polyurea or polyurethane material tocompletely coat the surface of the wax or wood structure. Cooling linesare placed within the box structure. After the polyurea or polyurethanematerial has dried/cured, aluminum puffs/pellets and an epoxy materialmix is then inserted into the cavities of the mold. Mold supportstructures and stanchions may be placed within the box to providestrength and stability to the polyurea or polyurethanes mold as well asto provide additional heat transfer material to the mold. Another layerof polyureas or polyurethanes may be sprayed within the mold. Afterdrying/curing, a vacuum plate is placed over the box structure providingexterior connections to the cooling lines as well as connections to thevacuum hole. The original wax or wood structure is then removed leavinga smooth mold surface made out of the polyurea or polyurethane materialand/or blends.

The resulting mold and its process provides a quick, inexpensive anddurable mold. Cooling lines are easily installed and eliminate the needof machining into steel or aluminum. Vacuum holes are able to be drilledthroughout the mold at a much faster rate than into steel or aluminum.The support structures provide a heat transfer element during themolding process in addition to providing support to the mold structure.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art when the followingdescription of the best mode contemplated for practicing the inventionis read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views, and wherein:

FIG. 1 is a perspective view of a wax pattern or form contained in a boxstructure;

FIG. 2 is a perspective view showing a polyurea or polyurethane layerbeing deposited on the wax pattern;

FIG. 3 is a perspective view showing cooling lines installed over thepolyurea or polyurethane material;

FIG. 4 is a perspective view showing a heat transfer and supportmaterial being deposited over the cooling lines;

FIG. 5 is a perspective view showing another polyurea or polyurethanelayer being deposited into the box structure;

FIG. 6 is a perspective view showing a covered plate being installedover the box structure;

FIG. 7 is a perspective view showing the mold being removed from the waxor wood form; and

FIG. 8 is a perspective view showing a completed mold piece.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The intent of the invention is to provide a mold as shown in FIG. 8 foruse at a manufacturing facility. The steps to provide the finished moldare shown in FIGS. 1-7.

According to one aspect of the invention, the characteristics of thefinal molded product are stored in a computer. A positive pattern or amold blank 10 is made based on these characteristics of the finishedmolded product. These characteristics are retrieved to shape a positivepattern mold blank 10 from a wax or wood block. A box structure 12 isbuilt around the positive mold blank 10 made of wax or wood materialsuch that the positive surface represented as 14 is oriented face up inthe interior of the box structure 12. After the box structure 12 isbuilt, the preferred step is to spray the interior positive surface 14with the polyurea or other predetermined material. But as analternative, the positive pattern surface 14 can be prepped forproviding vacuum holes to the final mold product before the positivesurface 14 is sprayed. That step is described hereinafter.

As can be seen in FIGS. 3 and 8, vacuum holes 16 are drilled orotherwise disbursed into the positive surface 14 of the mold blank 10.The vacuum holes 16 are very small, approximately 0.040 inches diameter.The holes 16 are drilled into the positive surface 14 of the mold blank10 such that wires 18 may be partially inserted into the holes 16 andextend upwardly into the interior of the box structure 12, above thepositive surface 14 of the mold blank 10.

In FIG. 2, the interior positive surface 14 of the wax pattern issprayed with preferably a polyurea material 20. The material may beapplied manually or by a robot 22. Similar material such as a polyureablend, polyurethane, or a polyurethane or urethane blend may be used.One of the advantages of using polyurea and the other mentionedmaterials is that the material provides a relatively quick cure time.That is after spraying, the material is dried within 20-30 seconds.Polyurea provides the quickest drying time and the best durability ofthe aforementioned materials. Further, these materials, and especiallypolyurea, provide excellent impact strength, stability at hightemperature, and surface quality. The spray polyurea or polyurethanematerial 20 may be tinted to a color such that when the material ismanually sprayed onto the wax pattern 10, the operating personnel knowswhen the entire positive surface 14 has been covered with the material20. The polyurea or polyurethane material 20 is applied as thin aspossible, less than one-eighth inch thick and preferably approximately0.060 inches thick. FIG. 2 shows the positive surface 14 partiallycovered by the polyurea material 20.

The polyurea material 20 dries within a half a minute so that coolinglines or tubes (heat transfer tubing) 24 may be installed soon after thepolyurea material 20 is applied. FIG. 3 shows the cooling lines 24installed within the box structure 12 over the first polyurea layer 20and mold blank 10. The cooling lines 24 are installed according to theshape of the mold blank 10. The cooling lines 24 are preferably made outof the copper tubing that meet in a pair of manifolds 26 providing aninlet 28 and outlet 30 aperture for later connection to an outsidecooling source. The size and configuration of the cooling lines 24 willdepend on the mold size and cooling or heating requirements.

In addition to the cooling tubing 24, metal pellets 32 such as aluminumcan be disposed within the box structure 12. Aluminum pellets 32 arepreferred because of their light weight and high heat transfercapabilities. The metal pellets or chips 32 are first mixed with anepoxy material 34 to provide some adhesion to the metal pellets 32 andprevent them from freely moving within the box structure 12. Looking aFIG. 4, the metal pellets 32 and epoxy material 34 can be poured orotherwise disposed into the box structure 12 over the cooling tubes 24such that the cooling tubes 24 are virtually covered with the pellets 32and epoxy 34 mixture. The metal pellets 32 and epoxy 34 mixture providesadded strength to the final mold, plus provides an additional form ofheat transfer. Although the cooling tubes 24 are virtually covered by thmetal pellet 32 and epoxy 34 mixture, the inlet an outlet apertures 28,30 respectively of the manifolds 26 remain exposed so that they may belater operatively connected to fluid lines. The metal pellet 32 andepoxy 34 mixture does not provide an impenetrable mixture and thereforemany air hole passages are available between the pellets 32 within themixture. This allows for the vacuum draw to reach the vacuum holes 16 inthe first layer of polyurea through the metal pellet 32 and epoxy 34mixture.

After the pellet and epoxy mixture is applied, the epoxy 34 is allowedto solidify. Looking at FIG. 5, it is shown that another layer 36 ofpolyurea or polyurethane material may be sprayed over the cooling lines24 and metal pellet 32 and epoxy 34 mixture. Again, the second layer ofpolyurea 36 or other similar material, as stated above, may be appliedthinly over the cooling lines 24 and metal pellet and epoxy mixture. Thesecond layer of polyurea material 36 may also be tinted to indicate thatthe entire surface has been covered with the polyurea material 36.

As shown in FIG. 6 further supports or stanchions 38 may be insertedinto the box structure 12 to provide added strength to the final mold. Avacuum plate or closure top 40 is then inserted and sealed over the boxstructure 12. The vacuum plate 40 has apertures 42, 44 corresponding tothe inlet 28 and outlet 30 apertures of the heat transfer manifolds 26.Further there is a third aperture 46 for accessing a vacuum source tothe interior of the box structure 12.

Generally, after the plate 40 is sealed onto the box structure 12, themold blank 10 and wires 18 providing vacuum holes 16, if applicable, tothe polyurea layers 20, 36 may be removed as shown in FIG. 7. The moldblank 10 and wires 18 can be discarded or used again. The box structure12 in FIG. 7 is turned over 180° to expose the final mold 50 as shown inFIG. 8. The fluid apertures 42, 44 and 46 are positioned at the bottomof the box structure 12 for later connection. If vacuum holes 16 werenot provided in the polyurea surface 20 via the wires 18 during themanufacture of the mold, the final mold 50 may be drilled once the moldblank 10 is removed. The drilled vacuum holes 16 are very small,preferably approximately 0.040 inches diameter. Drilling the vacuumholes 16 after the final mold 50 is completed is the preferred method.Drilling the vacuum holes 16 at the end saves steps plus eliminates theneed of the wires 18.

The resultant mold 50 provides a cost effective mold that can bemanufactured quickly, with a minimum of labor and material expenditures.The resultant mold 50 manufactured by the process as detailed above canbe available for use within a couple of days.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiments but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, which scope is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

What is claimed is:
 1. A mold form for an article comprising: a porouslayer of plastic resin having an article-forming surface and a secondsurface opposite from the article-forming surface, the plastic resinselected from the group consisting of polyureas, polyurea blends,polyurethanes, polyurethane blends, and mixtures thereof; heat transfertubing positioned adjacent the second surface; a porous mixture of metalpellets and epoxy positioned adjacent to the second surface and betweenthe heat transfer tubing permitting vacuum communication through theporous mixture and layer during vacuum forming of the article to bemanufactured; and a second layer selected from the group consisting ofpolyureas, polyurea blends, polyurethanes, polyurethane blends, andmixtures thereof, wherein said second layer substantially covers theporous mixture.
 2. The mold form of claim 1 further comprising anenclosure having at least one surface with apertures accommodating entryand exit of the heat transfer tubing.
 3. The mold form of claim 2,wherein the article-forming surface has small vacuum apertures formedtherein, and the at least one surface includes an aperture adapted tocommunicate with a vacuum source.
 4. A mold form for an articlecomprising: a layer of cured plastic resin having an article-formingsurface corresponding to a surface of the article to be manufactured anda second surface opposite from the article-forming surface, the layer ofcured plastic resin having a plurality of small vacuum apertures formedin and extending therethrough allowing passage of vacuum during vacuumforming of the article to be manufactured; and heat transfer tubingpositioned adjacent to the second surface of the layer of cured plasticresin, wherein the thickness of the layer of cured plastic resin is lessthan one-eighth inch thick.
 5. The mold form of claim 4 wherein thelayer of cured plastic resin is selected from the group consisting ofpolyureas, polyurea blends, polyurethanes, urethane blends, andpolyurethane blends.
 6. A mold form for an article comprising: a layerof cured plastic resin having an article-forming surface correspondingto a surface of the article to be manufactured and a second surfaceopposite from the article-forming surface, the layer of cured plasticresin having a plurality of small vacuum apertures formed in andextending therethrough allowing passage of vacuum during vacuum formingof the article to be manufactured; heat transfer tubing positionedadjacent to the second surface of the layer of cured plastic resin; anda porous layer including a porous mixture of metal pellets and epoxypositioned between the heat transfer tubing and adjacent to the secondsurface allowing communication between the source of vacuum and thearticle-forming surface wherein the layer of cured plastic resin is afirst layer, and further comprising a second layer of cured plasticresin spaced from the first layer of cured plastic resin with the porouslayer including the porous mixture of metal pellets and epoxy interposedtherebetween.
 7. The mold form of claim 6, wherein the metal pellets areformed from aluminum.
 8. The mold form of claim 6 further comprising thefirst and second layers of cured plastic resin selected from the groupconsisting of polyureas, polyurea blends, polyurethane, polyurethaneblends, and mixtures thereof.
 9. The mold form of claim 4, wherein theheat transfer tubing is formed from copper.
 10. A mold form for anarticle comprising: a layer of cured plastic resin defining anarticle-forming surface for vacuum forming an article to be manufacturedand a second surface opposite from the article-forming surface; heattransfer tubing positioned adjacent to the second surface of the layerof cured plastic resin; a layer containing a porous mixture of metalpellets and epoxy positioned between the heat transfer tubing andadjacent to the second surface of the layer of cured plastic resin; andvacuum passage means, formed in and extending through the layer of curedplastic resin and the layer containing the porous mixture of metalpellets and epoxy, for drawing vacuum therethrough while vacuum formingthe article to be manufactured, wherein the layer of cured plastic resinis a first coat, and further comprising a second layer of cured plasticresin applied over the layer containing the mixture of metal pellets andepoxy.
 11. The mold form of claim 10, wherein the layer of cured plasticresin is selected from the group consisting of polyureas, polyureablends, polyurethanes, urethane blends, and polyurethane blends.
 12. Themold form of claim 10, wherein the heat transfer tubing is formed fromcopper.
 13. The mold form of claim 10, wherein the metal pellets areformed from aluminum.
 14. The mold form of claim 10, wherein the secondlayer of resin is selected from the group consisting of polyureas,polyurea blends, polyurethanes, urethane blends, and polyurethaneblends.
 15. The mold form of claim 10 wherein the thickness of the firstand second coats of resin is less than one-eight inch thick.